Track merge request approval policy sync state

What does this MR do and why?

We are working on visualising the synchronisation status of merge request approval policies in the policy overview UI (#559273 (closed)).

This MR uses the callbacks introduced by !201777 (merged) to issue sync progress updates from services/workers.

References

• &19049
• #559273 (closed)

Screenshots or screen recordings

• #559273 (comment 2684732955)

How to set up and validate locally

echo "Feature.enable(:security_policies_csp)" | rails c
echo "Feature.enable(:security_policy_sync_propagation_tracking)" | rails c

1. Navigate to Admin > Settings > Security and compliance and under Compliance and security policy group, and select a group with an approval policy linked such as:

approval_policy:
- name: CSP any_merge_request
  enabled: true
  rules:
  - type: any_merge_request
    branch_type: protected
    commits: any
  actions:
  - type: require_approval
    approvals_required: 1
    role_approvers:
    - owner

2. Identify the CSP policy configuration's ID:

Security::OrchestrationPolicyConfiguration.for_namespace(
  Security::PolicySetting
    .for_organization(::Organizations::Organization.default_organization)
    .csp_namespace_id)
  .pluck(:id)
  .first

3. Subscribe to updates for the configuration as the sync progresses:

subscription {
  securityPoliciesSyncUpdated(policyConfigurationId: "gid://gitlab/Security::OrchestrationPolicyConfiguration/$CONFIGURATION_ID") {
    projectsProgress
    projectsTotal
    failedProjects
    mergeRequestsProgress
    mergeRequestsTotal
  }
}

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Related to #528300 (closed)